Raw GPS data decoding with RTKLIB

I was delighted to discover Tim Everett’s blog documenting the use of RTKLIB and uBlox GPS receivers. RTKLIB is an open source program that can be used to interpret raw GNSS GPS data, for example, to work out GPS positions from a batch of raw measurements at a later date vs in the field live.

I’ve been interested in raw GPS data for some time, as collecting the pesudo random code from GPS satellites in a raw format and figuring our locations later could possibly enhance the speed in which we can collect data at sea from our sea turtle tags (i.e collect the tag from a returning sea turtle and decode the GPS data when back in the office). Essentially, GPS satellites transmit signals on two carrier frequencies. One carries the status message and the second a pseudo-random code for timing. Collecting this information quickly (when a sea turtle comes up to take a breath) is therefore of particular interest to me.

There are a few issues in relation to using uBlox modules however, as it looks like moves have been made to limit access to raw data. I’m currently exploring the options avaiable, but an optimised standard uBlox module (NEO or ZOE for example) that is also pre-loaded with almanac tables also remains a key focus.